1. Field of the Invention
The present invention relates to a method of achieving improved productivity in the manufacture of printed circuit boards. The improved productivity occurs because of increasing the efficiency and data accuracy of an inspection cycle.
2. Description of the Prior Art
Most types of electronic equipment produced today incorporate one or more printed circuit boards which have various types of electronic components thereon. As electronic equipment becomes more and more complex, printed circuit boards are being designed which have a greater density of components. As component density increases, inspection of the printed circuit boards, throughout the manufacturing process, becomes much more difficult. Human operators have experienced greater difficulty in visually inspecting the printed circuit boards for defects. Occasionally, even an experienced operator will fail to detect defects in the form of a missing or misinserted component. Also, visual inspection by human operators must be performed at a relatively slow speed and may be affected by the operators susceptibility to fatigue.
Because of the difficulties associated with visual inspection of printed circuit boards, much effort has been devoted to developing automatic equipment for performing this task. Although these automatic systems work well, these systems incorporate line scan vision cameras or television cameras which are extremely expensive and complicated.
U.S. Pat. No. 4,005,939 Aby Stavalone, U.S. Pat. No. 4,105,340 by Kempf and U.S. Pat. No. 4,379,647 by Kempf disclose apparatuses for optically comparing a manufactured board with a master board to identify a discrepancy on the manufactured board because of its different appearance from the master board. The image comparison is made by an observer who scans the alternately presented images. The effectiveness of this comparison is dependant on the skills of the observer and the observer's susceptibility to fatigue. This method differs from the present invention because it relies on an observer and because this method cannot be automated or otherwise performed by mechanical or electrical means.
U.S. Pat. No. 4,295,198 by Copeland et al. describes a method and an apparatus of optically recognizing particular features of a printed circuit board (PCB) and then display that information on a CRT screen so an operator may create machine instructions for those features at specific locations. The instructions are then used to direct the operations of a numerically operated machine such as a gang drill. The present invention differs from this patent in that the present invention illuminates the PCB and uses unique materials in different patterns to uniquely characterize the sensed reflected radiation to permit either visual, optical or mechanical identification of a components presence, absence or orientation.
U.S. Pat. No. 4,549,206 by Suzuki et al. and U.S. Pat. No. 4,811,410 by Amir et al. disclose inspection systems for printed circuit boards. The systems illuminate the board and analyze the reflected light to determine various defects. The present invention is similar to these patents only in the fact that the present invention utilizes a means of illuminating the PCB and uses the reflected light. This is the same procedure used for any type of visual inspection. The present invention differs in that it employs unique materials in differing patterns to characterize the sensed light to permit either visual, optical or mechanical identification of component presence, absence, orientation or identity.
Because of the problems stated above, a method has been developed which minimizes the possibilities for error and also allows the inspector to increase the number of printed circuit boards inspected over a period of time, or to permit the use of automatic equipment to perform this task.